Means for inductively heating narrow elongated portions of cylindrical bodies



March 9, 1954 BODY 2,671,846

MEANS FOR INDUCTIVELY HEATING NARROW ELONGATED PORTIONS OF CYLINDRICAL BODIES Filed Feb. 28. 1950 2i INVENTOR 41/750 0 Booy 14 7' roe Y Y Patented Mar. 9, 1954 MEANS FOR INDUCTIVELY HEATING NAR- ROW ELONGATED PORTIONS OF CYLIN- DRICAL BODIES Alfred 0. Body, Cleveland, Ohio, assignor to The .Ohio Crankshaft Company, Cleveland, Ohio, a

corporation of Ohio Application February 28, 1950, Serial N 0. 146,888

This invention pertains to the art of highfrequency induction heating and, more particularly, to a high-frequency inductor adapted to heat narrow portions or hands on elongated metallic members.

The invention is particularly applicable to the field, of heating the close-spaced opposite edges of a generally c-shaped metallic strip prior to welding the strip into pipe and will be so described hereinafter. Also, the strip will be referred to for the purposes of convenience as pipe, although it is appreciated that it is not pipe until the final welding of the edges has been completed.

The invention is, in some respects, an improvement on the high-frequency inductor shown and described in the copending application of Phillips N. Sorensen, Serial No. 86,066, now abandoned. In that application, there is shown a high-frequency inductor for heating the close-spaced edges of pipe to the welding temperature comprisin generally: a main branch adapted to be disposed in close-spaced parallel relationship with the edges; a pair of side conductors parallel to the main branch and spaced therefrom and adapted to be in generally close-spaced relationship to the sides of the pipe spaced from the edges; and, end conductors connecting the side conductors in electrical parallel relationship and in series electrical relationship with the main branch. 'The main branch is divided at the center and the high-frequency power is fed into the inductor at this point by a pair .of fish-tail leads. Also, the main branch had a Stack of laminations along its entire len th except where the fish-tail leads connectedthe ieto.

In the inductor of Sorensen, when applied to conventional pipe seam-welding equipment, the over-all length of the inductor was limited.

Accordingly, in order to obtain high pipe speeds, it was necessary to use Very high-power densities in the inductor itself. With the Sorenen inductor, when the power was fed into the main branch, there resulted an approximate loss of between one to two inches of effective heating length of the main branch. With a ten-inch inductor, this is a reduction in the effective heating length of between ten and twenty per cent.

The present invention contemplates an inductor of the general type referred to wherein the high-frequency energy is fed into the inductor at points other than in the main branch and, particularly, into the side legs.

The invention also contemplates providing .physicalmeans extending from the fish-tail leads to the :main conductor tor-the purpose of sun- Claims. (C1. 219-10.53)

porting same and make the inductor more rigid and resistant to the magnetic pull between the pipe and the inductor.

The invention also contemplates an inductor wherein the side conductors are relatively loosely coupled with the sides of the pipe and are relatively large in cross-sectional area compared to the main conductor so as to provide a loose coupling with the pipe over a substantial area thereof remote from the edges to be heated.

It is an object oi the invention to provide a high-frequency inductor which is rigid in construction; efiicient electrically; which, for a given t has a maximum effective heating length and which is readily cooled.

Another object of the invention is the provision of an inductor having parallel main and side conductor branches, the side conductors being split and with fish-tall leads connecting to the side conductors on opposite sides of the split.

Another object is to provide such an inductor with physical means from the fish-tail leads to the center branch for the purpose of giving struc.- tural rigidity to the entire inductor.

Still another object of the invention is the provision of a high-frequency inductor of the type referred to wherein the side conductors are of a maximum area and are loosely coupled with the sides of the pipe.

The invention may take physical shape in a number of diiferent forms, all of which may differ radically in appearance one from the other. In order to describe the invention, a preferred embodiment will be specifically described in this specification and illustrated in the accompany.- ing drawings which are a part hereof, and

wherein:

Figure 1 shows a side elevational view, with portions broken away for the purposes of clarity, of a high-frequency inductor embodying the present invention;

Figure 2 is a sectional view on the line 21-2 of Figure 1;

Figure 3 is a fragmentary sectional view on the line 3-3 of Figure 2;

Figure 4 is a fragmentary top elevational view of Figure 1 taken approximately on the line 11-4 of Figure l; and

Figure 5 is a fragmentary sectional view taken approximately on the line ti -e5 of Figure 1.

Referring now to the drawings wherein the preferred embodiment is shown for the purposes of illustration only and not for the purposes of l mitation, igure .1 and 2 Show a p peA being 3 moved progressively through a high-frequency inductor energized from a source of high-frequency energy not shown.

The pipe A forms no part of the present invention and is shown for the purposes of more clearly illustrating the invention.

In general, however, the pipe is generally shaped in cross section and has a pair of closespaced edges III which are to be heated to a welding temperature and, subsequently brought into pressure abutting relationship.

The inductor shown comprises a main branch indicated generally by the reference numeral II,

a pair of side conductors I2 and end conductors I3, a pair of fish-tail leads I4 and terminal blocks I5 which are adapted to be connected to matching terminal blocks on a transformer not shown.

The main branch II is the principal heat-inducing portion of the inductor and comprises generally an elongated straight conductor I6 having a generally trapezoidal cross-sectional shape with the narrower of the two parallel surfaces forming the pipe edge-adjacent surface thereof. This conductor is also hollow throughout its entire length so that the cooling water could be circulated therethrough.

The'remaining three surfaces of the conductor I6 are closely surrounded by magnetically permeable material ll of sufiicient transverse thickness to carry the magnetic flux about the conductor I6 without saturating or overheating. The material II in the embodiment shown is comprised of a stack of thin flat laminations having their principal plane transverse to the length of the conductor IS. The laminations are electrically insulated one from the other by a thin film of insulation (not shown). The small dimension of the laminations measured in the direction of the current travel in the conductor I6 and the insulation between the individual 1aminations each contribute to a minimum of current flow and, thus, heating in the material.

It will be noted that the entire main branch extends parallel to and in close-spaced relationship to the edges ID. As the pipe A moves through the inductor, the flux of the conductor I6 enters the pipe A and generates high-frequency, high-concentrated electric currents to flow longitudinally in the edges I0 and rapidly heats these edges to a welding temperature.

The side conductors I2 are generally rectangular in cross-sectional shape, although they may be otherwise. They are also hollow to permit the flow of cooling water therethrough. As shown, the major dimension of the rectangular shape is somewhat greater than the diameter of the pipe to be heated and extends on a diverging angle from a horizontal plane slightly below the surface of the pipe A to a point slightly above the upper edge of the pipe A. As will be noticed, they are spaced a substantial distance from the sides of the pipe over their entire width. The lower edges of the side conductors I2 are, however, spaced a suificient distance apart so that the entire inductor can be removed from the vicinity of the pipe A by movement transverse to the axis of the pipe.

As shown, the side conductors I2 are divided transversely at the center and spaced slightly as I9. A sheet of suitable insulation 22 is positioned between each fish-tail lead I4 and extends downwardly to also insulate the adjacent ends of the side legs I2 and fill the gap I9. As shown, the fish-tail leads substantially clear the outer periphery of the laminations I! so that any flux field around the laminations will-not and cannot link with any flux field which may be exterior to the fish-tail leads I4 and, particularly, in the space between the fish-tail leads I4 and the main branch II.

In some instances, and with the construction shown, difficulty has been experienced due to the lack of suilicient rigidity in the inductor. The magnetic field about the main branch II tends to draw the pipe A and the main branch II toward each other with a considerable force. In order to provide rigidity to the entire inductor to withstand these magnetic forces, physical-support means are provided directly from the fishtail leads to the main branch I I to give the main branch support at least at some point along the length other than at the ends. Such means may take a number of different forms. In the embodiment shown, however, the insulating member 22 between the fish-tail leads I4 extends downwardly between and beyond the legs 20 and has an opening therein through which the conductor I5 extends and fits snugly. The laminations at this point are separated to permit the insulating plate 22 to fit around and engage the conductor I6. The plate 22 could be positioned over the laminations so as not to cause any interruption in the continuity thereof. With such an arrangement, the magnetic pull on the main branch II may be transmitted directly to the fish-tail leads over a minimum length of material and, thus, provide an inductor with a maximum of rigidity. It would be appreciated that, if necessary, gusset plates (not shown) could extend from the fish-tail leads outwardly in a plane parallel to the main branch II to provide additional support for its entire length. Other means of support could be provided.

The fish-tail leads I4 terminate at their upper end in terminal blocks I5 which are suitably shaped to end in terminal blocks on an impedance-matching transformer (not shown) connected to a suitable high-frequency power source. The transformer terminal blocks are not shown, but they constitute the means of support for the inductor shown.

The terminal blocks have fish-tail leads preferably hollow so that water or other cooling medium may be circulated through the interior of the inductor. Inlet ports 24 are shown for the purposes of providing access to circulate cooling medium through the interior passages of the inductor.

The end conductors I3 extend generally horizontally at each end of the inductor and transversely to the length of the conductors II, I2. The ends of the conductors I3 are rigidly connected to the ends of the conductor I2 while the ends of conductor II are connected to the mid point of conductors I3. As shown, the vertical height of the end conductor is approximately the same as the vertical height of the conductor II and the magnetic material I'I extends above the upper surface of the end conductor I3. Also, the portion of the material I1 on both sides of the conductor II faces the conductor I3. The flux about the conductor I3 thus normally would tend to enter the laminations and generate currents in a major dimension of the laminations and will effect heating.

A flux shield is provided at the ends of the laminations adjacent the conductors It to force this flux to enter and leave the laminations in the plane thereof, thus not inducing any current flow in loops other than in a plane transverse to the plane of each lamination. As the laminations are very thin; the current in such a loop can, at best, be small and, thus, produce little heating.

The preferred embodiment shows the end lamination of the stack of laminations formed of a copper sheet 26 which has external dimensions at least as great as the magnetic lamination's; and, in the vertical dimension, exceeds the vertical height of the laminations and, thereby, extends above the lamina-tions and tends to shield the 'laminations not only at the very ends of the stack but the laminations near the ends. This construction is described and claimed in the copendi-ng application of James W. Williamson, Serial No. 384,546, filed October 7, 1953.

The inductor shown has proven extremely practical for the purpose of heating the edges of pipe prior to their being brought into pressurewelding engagement. It provides a maximum length of effective heating for a given over-all length of inductor, it provides a maximum rigidity, it allows the inductor to be positioned in a welding machine and removed with the pipe to be heated in its heating position. The inductor and laminations operate cool. The problem of cooling of the center leg is extremely mitigated due to the straight-through passage of cooling water.

The invention permits'similar improvements in inductors intended for other purposes.

In the specification and claims, the terms close coupling and loose coupling are employed. By close coupling is intended that type of electrical coupling with the workpiece which is governed mostly by the physical operation of the machine such that there is no danger of the workpiece striking the inductor in commercial usage. This distance in many practical instances is in the neighborhood of of an inch. It may be closer and would be so if conditions permitted. It is preferably never greater than twice that amount. By loose coupling, it is meant any spacing of the conductors a distance greater than ten times the close coupling space employed.

It can be appreciated that theinductor described above is only one embodiment of a large number which may result from the present invention. Other embodiments will occur to others upon a reading and understanding of this specification. It is our intention that all such modi- *fications, insofar as they come within the scope of "the appended claims, shall be included as part of the invention.

Having thus described my invention, I claim:

1. A high-frequency inductor comprising a main branch and a pair of side conductors, said side conductors being disposed in close-spaced parallel relationship with said main conductor, said side conductors being divided intermediate the ends thereof and fish-tail leads connected to saidside conductors on each side of the division thereof, and a pair of end conductors, one at each end of and connecting said main and side conductors in electrical parallel relationship.

2. A high-frequency inductor comprising a main conductor and a pair of side conductors,

said side conductors extending in spaced parallel relationship to said main conductor and generally in a plane below said main conductor, .each of said side conductors being divided transversely intermediate "the ends thereof, .a pair :of fishtail leads being positionedgenerally above .said main conductor and having a pair of legs extending downwardly on each side of said main conductor, said legs connecting with said .side conductors on each side of the division thereof, and a pair of end conductors, one at each end of and connecting said main and side conductors in electrical parallel relationship.

3. The combination of claim '2 *wherein physical meansare associated with said rish-tai-lvleads and said main conductor midway between its .ends for the purpose of physically strengthening same.

4. A high-frequency inductor comprising .a main conductor and a pair of side conductors, one on each side of said main conductor and parallel thereto, said side conductors being :divided intermediate the :ends thereof, fish-tail leads connected to each side of the division of said conductors and extending over said main conductor, and electrically 'insulating material rigidly interconnecting said fish-tail leads and said main conductor.

A high-frequency inductor past which an axially split tube is to be continuously moved to have its edges adjacent the split progressively heated to a welding temperature, said inductor comprising: a main conductor; a pair of side conductors, one on each side of said main conductor and symmetrically disposed relative thereto; a pair of end conductors extending transversely to and electrically connected to respective endsof said main and side conductors to connect said conductors in an electrical parallel circuit; said main conductor having-a generally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having geenrally wide workpiece-facing surfaces generally facing each other and spaced apart a distance greater than that of the tube to be welded, the extended planes of the respective workpiece-facing surfaces forming a generally inverted, U-shaped channel through which the tube passes, with the width of the channel being substantially greater than the diameter of the tube.

6. A high-frequency inductor past which an axially split tube is to be continuously moved to have its edges adjacent the split progressively heated to the welding temperature, said inductor comprising: a mainconductor; -a pairof side conductors, one on each side of said main conductor and symmetrically disposed relative there to; a pair of end conductors extending transversely to and electrically connected to respecti-ve ends of said main and side conductors to connect said conductors in an electrical parallel circuit; said main conductor having agenerally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having workpiece-facing surfacesgenerally facing each other and spaced apart 'agreater distance than the diameter of said tube, the area of the workpiece-facing surfaces of said side conductors being substantially greater than the workpiece-facing area of said main conductor, the extended planes of the respective workpiecefacing surfaces forming a, generally inverted U- shaped channel through which "the tube "is 7 adapted to pass, the width of the channel being substantially greater than the diameter of said tube.

7. A high-frequency inductor past which an axially split tube is to be continuously moved to 'have its edges adjacent the split progressively 7 conductors in an electrical parallel circuit; said main conductor having a generally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having workpiece-facing surfaces generally facing each other and spaced apart a distance greater than that of the tube to be welded; the extended planes of the respective workpiece-facing surfaces forming a, generally inverted, U-shaped channel through which the tube passes, with the width of the channel being substantially greater than the diameter of the tube; said side conductors each being comprised of two portions in aligned end-to-end relationship with an insulating gap therebetween; and, conductors connected to said portions immediately adjacent the gap and extending away therefrom in insulated close-spaced relationship and means interconnecting the conductors associated with the respective ends of said inductor in electrically parallel relationship. 8. A high-frequency inductor past which an axially split tube is to be continuously moved to have its edges adjacent the split progressively heated to a welding temperature, said inductor comprising: a main conductor; a pair of side conductors, one on each side of said main conductor and symmetrically disposed relative thereto; a pair of end conductors extending transversely to and electrically connected to respective ends of said main and side conductors to connect said conductors in an electrical parallel circuit; said main conductor having a generally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having workpiece-facing surfaces generally facing each other and spaced apart a distance greater than that of the tube to be welded, the extended planes of the respective workpiece-facing surfaces forming a generally invverted, U-shaped channel through which the tube passes, with the width of the channel being substantially greater than the diameter of the tube; each side conductor being comprised of two aligned portions in end-to-end relationship with an insulating gap therebetween and a pair of lead conductors in close-spaced, insulated relationship; said lead conductors extending away from said inductor on the side opposite from the workpiece-facing surface of said main conductor and having a substantial width in a direction transverse to the length of said main conductor; each of said lead conductors having a pair of depending spaced legs connecting respectively to the portions forming said side conductors immediately adjacent said insulating gap. H 9. A high-frequency inductor past which an axially split tube is to be continuously moved to have its edges adjacent the split progressively heated to a welding temperature, said inductor comprising: a main conductor, a pair of side conductors, one on each side of said main conductor and symmetrically disposed relative thereto; a pair of end conductors extending transversely to and electrically connected to respective ends of said main and side conductors to connect said conductors in an electrical parallel circuit; said main conductor having a generally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having workpiece-facing surfaces generally facing each other and spaced apart a distance greater than that of the tube to be welded, the extended planes of the respective workpiece-facing surfaces forming a generally inverted, U-shaped channel through which the tube passes, with the width of the channel being substantially greater than the diameter of the tube; each side conductor being comprised of two aligned portions in end-to-end relationship with an insulating gap therebetween and a pair of lead conductors in close-spaced, insulated relationship; said lead conductors extending away from said inductor on the side opposite from the workpiece-facing surface of said main conductor and having a substantial width in a direction transverse to the length of said main conductor; each of said lead conductors having a pair of depending spaced legs connecting respectively to the portions forming said side conductors immediately adjacent said insulating gap; and, insulating means extending between said lead conductors and said main conductor and rigidly attached to each.

10. A high-frequency inductor past which an axially split tube is to be continuously moved to have its edges adjacent the split progressively heated to a welding temperature, said inductor comprising: a main conductor; a pair of side conductors; one on each side of said main conductor and emmetrically disposed relative thereto; a pair of end conductors extending transversely to and electrically connected to respective ends of said main and sid conductors to connect said conductors in an electrical parallel circuit; said main conductor having a generally straight, elongated, narrow, workpiece-facing surface adapted to be disposed in close-spaced relationship to said edges; said side conductors each having workpiece-facing surfaces generally facing each other and spaced apart a distance greater than that of the tube to be welded; the extended planes of the respective workpiece-facing surfaces forming a generally inverted, U-shaped channel through which the tube passes, with the width of the channel being substantially greater than the diameter of the tube; each side conductor being comprised of two aligned portions in end-to-end relationship with an insulating gap therebetween and a pair of lead conductors in close-spaced, insulated relationship; said lead conductors extending away from said inductor on the side opposite from the work piece-facing surface of said main conductor and having a substantial width in a direction transverse to the length of said main conductor; each of said lead conductors having a pair of depending spaced legs connecting respectively to the portions forming said side conductors immediately adjacent said insulating gap; said main conductor having a generally trapezoidal cross section and insulating means rigidly fixed to said lead conductors and extending to said main conductor; said insulating means having a trapezoidally shaped opening through which said main conductor extends, whereby to provide a rigid connection between said insulating means and said main conductor.

ALFRED C. BODY.

References Cited in the file of this patent 5 UNITED STATES PATENTS Number Name Date 2,073,597 Northrup Mar. 9, 1937 2,299,934 Sherman et a1 Oct. 27, 1942 2,428,303 Wood Sept. 30,1947 10 ,448,690 Storm Sept. 7, 948

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